It is known that routine maintenance of structures is necessary to prevent them from deteriorating to a point where they must be replaced rather than repaired. Bridges, in particular, require such routine maintenance but many are in extremely poor condition. Many bridges have been closed and torn down because they are unfit for safe passage. Replacement of bridges is expensive and wasteful. Routine repair is a more economical and sensible approach.
There are two fundamental impediments to conducting routine bridge maintenance. It is difficult to put men and equipment up in the air on a large bridge structure where they are exposed to the weather without risking their safety and without interrupting traffic. It is also difficult to ensure that the detritus from cleaning, scraping and painting will not contaminate soil and water surrounding the bridge. As a result bridge maintenance is often postponed or avoided and deterioration continues. The prior art discloses some equipment and methods relating to bridge maintenance but the problem of deteriorating bridges continues.
U.S. Pat. No. 5,011,710 entitled "BRIDGE MAINTENANCE METHOD AND EQUIPMENT" dated Apr. 30, 1991, describes a method in which surfaces of a structure are treated from a walkway within an enclosure suspended from the structure. The enclosure has a downwardly-converging cross section terminating in a vacuum conveyor for collecting and removing particles accumulating from the blasting process. The enclosure is preferably provided in modules. The vacuum conveyor removes the particulate material for transfer to conventional separating and re-cycling equipment. The enclosure and walkway are movably suspended from transverse guides secured to the structure. Similarly, U.S. Pat. No. 4,854,419 entitled "PARTICULATE CONTAINMENT CONTROL METHOD AND PLATFORM DEVICE" dated Aug. 08, 1989, describes a mobile containment platform method and system for sandblasting and the like used in bridge reconditioning and painting that requires removal of paint from the support structure of the bridge. The containment platform provides an entrapment envelop for spent abrasive and removed paint residue.
U.S. Pat. No. 4,201,275 entitled "MEANS FOR THE RENOVATING AND REFURBISHING OF OVERHEAD STRUCTURES" dated May 06, 1980, describes a method for furbishing or renovating large span overhead structures, for example the roofs of railway stations, or bridges and the like. It utilizes apparatus which comprises a plurality of runway beams suspended in spaced parallel disposition from the main ribs or framework of an overhead structure, the beams spanning a plurality of said ribs or framework and being longitudinally displaceable relative thereto, and a work platform or platforms suspended from said runway beams and being displaceable along the runway beams. Thus arranged, the overhead structure can be treated for substantially its entire length by alternately advancing the work platforms along the runway beams and the runway beams relative to the structure.
U.S. Pat. No. 4,848,516 entitled "MOVABLE SCAFFOLD" dated Jul. 18, 1989, describes a movable scaffold has a pair of hanger rails attached to a construction, first hanger units movably mounted on the hanger rails, beams operatively engaged with the first hanger units and laterally disposed with respect to the hanger rails, and a floor deck mounted on the beams. Second hanger units are provided for movably suspending the beams from the first hanger units.
German patent DD 241626 dated Dec. 17, 1986, describes an apparatus to enable a bridge to be painted without erecting a complete scaffold, and enabling road and rail traffic to continue to use the bridge. A roller grid is used, which can be slid the whole length of the bridge. It has an upper frame with a fixed wheel and a lower frame supported by a fixed roller on the bridge structure and attached to the upper frame.